A. Technical Field
This invention relates generally to optical communication networking systems, and more particularly, to the transmission of high speed client signals across a transport network.
B. Background of the Invention
The capacity of transport systems is continually increasing to provide larger amounts of available bandwidth to clients. These transport systems are able to communicate large amounts of data using optical networking technologies. In certain systems, wavelength division multiplexed (hereinafter, “WDM”) transport systems communicate this data on multiple wavelengths between terminal nodes. These WDM systems offer a network provider scalable bandwidth without having to significantly expand the physical infrastructure of a network to realize this additional bandwidth.
Certain transport systems are designed to receive a client signal, re-format the client signal and transmit this reformatted client signal over a long-haul connection. The client signal is subsequently reconstructed at a receiver in the transport system and delivered to the client network. The transport system may operate in accordance with various standard protocols, such as the Optical Transport Network (hereinafter, “OTN”) protocols, or proprietary formats and procedures.
Transport systems are designed to interface with various types of client networks. In so doing, the transport system maps data from a client signal into a transport frame in which the data propagates across a transport connection. This mapping procedure is typically specific to the protocol of the client signal and the format of the transport system so that the client signal may be completely reconstructed at a transport receiver. The transport terminal nodes, both transmitter and receiver nodes, are generally able to operate in different modes depending on the type of client signal that is being processed. For example, a transport terminal node may map a client SONET frame into a transport frame using a first mapping procedure or an Ethernet frame into a transport frame using a second mapping procedure.
The transmission characteristics of the client data across the transport connection may depend on both the protocol and rate of the particular client signal. If a client signal is transmitted at a higher rate than the channel rate of the transport system, then the client data is transmitted across multiple channels in the transport system. This multi-channel transmission of client data preserves the rate of the client signal and allows efficient reconstruction of the client signal at a transport receiver node.
Transport technologies have been and are currently being developed to enable efficient communication of this client data on a transport system. In certain transport systems, the client data is transmitted across the transport system on multiple wavelengths. As a result, legacy transport networks are able to adapt to the ever-increasing optical signaling rates by dividing the client signal across multiple wavelength channels within the transport network. For example, there are many transport networks currently deployed that communicate 10 Gbps wavelengths within a WDM transport signal. A 40 Gbps client signal may be transmitted across this transport network by dividing the client signal into at least four channels. These channels are mapped within frames of the transport network and optically multiplexed into a WDM signal. The WDM signal is received at a network receiver and the client signal is reconstructed from the channels.
FIG. 1 generally illustrates an exemplary WDM transport transmitter. The transmitter receives a client signal 115 that has a higher rate than the transport network rate. If the client signal 115 is an optical signal, then an O/E converter 130 converts it to a corresponding electrical signal 117. A demultiplexer 120 demultiplexes the electrical signal 117 into a plurality of electrical channels.
Each of the electrical channels is coded and mapped into a transport frame. For example, a first channel is provided to a first coder/processing module 140 that encodes, and otherwise processes, the data within the first channel in preparation for framing. The first coder/processing module 140 may also insert error correction information within the first channel. A framer 150 maps the coded data and error correction information into transport frames in preparation for transmission across the transport network.
After framing, an E/O converter 160 converts the framed data and information within the first channel to an optical transport signal on a unique wavelength. The rate of this optical transport signal is equal to the rate of the transport network, which as previously discussed, is less than the rate of the client signal received at the transmitter input.
The optical transport signal is multiplexed by an optical multiplexer 170 with other optical transport signals generated from other channels within the transmitter. These other optical transport signals include, but are not limited to, other channels containing data that was demultiplexed from the client signal. The optically multiplexed transport signals comprise a WDM transport signal 175 that is communicated across the transport network.
Network redundancy is important to ensure the integrity of the client signal as it is being transported within the transport network. This network redundancy should be present at both inter-nodal and intra-nodal levels so that a failure event does not destroy a client signal. An intra-nodal failure may be a non-operational component within a node, such as the WDM transport transmitter described above, resulting in one or more channels being lost therein.